Gasoline-fueled motor vehicles have many sites from which hydrocarbons (HC) may evaporate into the environment. HC in the atmosphere is a major contributor to smog formation. One such known site is the intake manifold of an engine. As HC emission regulations are tightened, a mechanism is needed to prevent HC vapor from escaping from the intake manifold after engine shutdown. Known approaches have included, among others, closing off the intake and idle air with the throttle valve when the engine is shut off; adding a rigid monolith structure formed of activated carbon into the intake air flow path of the air cleaner (see U.S. Pat. No. 6,692,551 B2); and lining the intake manifold, other air ducts, and/or the air cleaner with adsorptive carbon sheeting.
Closing the intake and idle air with the throttle valve requires that the engine be equipped with electronic throttle control; many inexpensive engines are not so equipped. Further, so employing an engine's electronic throttle control may impair the desirable option of so-called “limp home” mode in which a vehicle may be driven in event of a partial failure of the engine electronics control system.
Carbon sheeting applied to inner surfaces of the manifold and air ducts is only partially successful because some HC laden air could escape the manifold without being brought into proximity with an adsorptive surface. Relatively large areas of carbon sheeting are required to ensure that an adequate quantity of HC comes into contact with the adsorber.
An adsorptive rigid monolith formed from activated carbon is unsatisfactory as it is expensive to fabricate, brittle and therefore vulnerable to breakage during assembly and use, and inherently restricts the flow of intake air. A known carbon monolith has an open area of only about 80%. The last shortcoming is especially undesirable as both engine performance and fuel efficiency can be adversely affected by undue air flow restriction.
What is needed in the art is a means for providing hydrocarbon adsorption during engine shutdown near the main air entrance to an engine while minimizing intake air restriction during engine operation.
It is a principal object of the present invention to reduce hydrocarbon emissions from a shut down internal combustion engine.
It is a further object of the invention to minimize the restriction of combustion air inflow into the engine caused by a hydrocarbon-adsorptive device.